As Star Gold you will get lounge access if you are departing on a Star-A flight.
Or you can get RCC access if you are an RCC member.

Generally, flying economy, you have access to the RCC (which is closer to the UA gates); or the ANA lounge (closer to ANA/SQ gates)

Each have their advantages.
I like the UA RCC for the views.
The ANA lounge has places in the back with reclining chairs to sleep.

ANA lounge showers has the fancy heated toilet seat; whereas UA RCC showers have the better soap/shampoo.

ANA lounge has a noodle bar as well.
THere are plenty of threads on this topic.